| With the development of science and technology,industrial equipment gradually has the trend of Miniaturization and microminiaturization.Microchemical technology has become an emerging interdisciplinary,and the gas-liquid two-phase flow in corresponding small pipes has also received more and more attention,compared with conventional pipes,the area/volume ratio of small pipes is greatly increased,and the transmission effect is improved by 2 to 3 orders of magnitude compared to conventional-sized pipes.It has the advantages of flexibility,efficiency,and integration.However,compared with conventional pipelines,the influence of surface tension and viscous force of small pipelines is significantly enhanced,which means that some of the flow characteristics and parameter changes in small pipelines are different from conventional pipelines.At present,the two-phase flow parameter measurement technology of small pipelines is still in the development stage,lacking the theoretical basis and mechanism model of the system.Through experimental comparison,the analysis of the similarities and differences between the characteristic parameters of the conventional pipeline and the small pipeline,such as the gas flow rate and void Fraction,can provide a reference for the development of the two-phase flow in the small channel,and has practical application prospects and research value.In view of the above research status,this paper studies five horizontal tubes with different inner diameters(10.45 mm,8.74 mm,6.68 mm,4.75 mm,3.12 mm).The main work and innovations are as follows:1.In the aspect of flow pattern recognition,a speed camera is used to obtain a two-phase flow pattern characteristic image,and a horizontal pipe two-phase flow parameter measurement system is built for the flow pattern characteristics of a horizontal pipe.The system includes water supply system,gas supply system,experimental section and data acquisition system.Through experiments,it was found that four typical flow patterns of bubble flow,slug flow,annular flow and laminar flow were found in horizontal tubes with 10.45 mm,8.74 mm and 6.68 mm inner diameters.No laminar flow was found in the 4.75 mm and 3.12 mm ID pipes.By comparison,it is found that the pipe diameter has a very important effect on the flow pattern transition boundary curve.By processing the pressure drop signal measured in the experiment,it is found that the fluctuation image of the pressure drop signal over time and the PDF image of the pressure drop signal can accurately predict the four typical flow patterns.2.In terms of void fraction measurement,it is based on a virtual binocular vision system,that is,the flow pattern of the bottom view of the visual measurement section is reflected horizontally into the focal plane of the camera by light reflection through the prism,and the camera captures the characteristic image of the flow pattern at the vertical angle.Image pre-processing is performed on the flow pattern map to obtain an operational binary image pair.Three-dimensional reconstruction is performed according to different flow pattern flow mechanisms and phase distribution characteristics,and the void fraction is calculated based on the three-dimensional reconstruction model.By comparing the 6.68 mm,4.75 mm,and 3.12 mm ID pipes with the calibrated void Fraction,the three-dimensional reconstruction method was used to calculate the void Fraction of the two-phase flow.The reliability of the new gas rate method.3.For the recognition of void fraction flow pattern based on image processing,the binary flow pattern image is used to measure the cross section void fraction,and the cross section void fraction fluctuation image with time and the cross section void fraction PDF image are used for flow pattern identification.The results show that the cross-sectional void fraction fluctuation image can accurately predict intermittent flow and continuous flow.There is no clear difference between bubble flow and slug flow,cross section gas rate signal and PDF fluctuations.4.In the evaluation of the void fraction prediction model,the void fraction prediction model is mainly divided into slip rate structure,KaH structure,drift flux structure and general empirical formula structure.Use the void fraction data in this paper to evaluate the existing void fraction prediction model,using three methods of evaluation:absolute error,root mean square error and cut-off parameter.It was found that most of the prediction models of void fraction are based on air-water,which is the same as the experimental working fluid in this paper,so all four structures show good prediction performance.Among them,the Smith model in the slip rate structure,the Chisholm model in the KaH structure,the Gregory and Scott model in the drift flux structure,and the Huq and Loth model in the empirical formula structure have good prediction results.Finally,the Gregory and Scott model based on the drift flux structure is modified by adding correction factors.The results show that for the void fraction under the working conditions in this paper,the prediction capacity of the improved void fraction model has greatly increased. |
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